1. Technical Field
The present invention relates to a very thin magnetoelectric transducer, and more specifically, to a small magnetoelectric transducer which allows the correctness of its mounting to be determined without being destroyed and that allows magnetoelectric transducers to be easily formed.
Furthermore, the present invention relates to a method for producing a very thin magnetoelectric transducer, and more specifically, to a method for producing a small magnetoelectric transducer which allows the correctness of its mounting to be determined nondestructively and that allows magnetoelectric transducers to be easily formed.
2. Background Art
Hall elements, which are among the magnetoelectric transducers, are widely used as rotational position sensors for drive motors for VTRs, flexible disks, CD-ROMs, and the like or as potentiometers or gear sensors. Owing to the trend to reduce the sizes of these electronics, there is a growing demand for a reduction in the thickness of Hall elements.
The current common Hall elements are produced as follows: First, a magnetoelectric transducer is constructed that is composed of a thin semiconductor film that has internal electrodes and that senses magnetism. Then, the magnetoelectric transducer is secured to a portion call an xe2x80x9cisland portionxe2x80x9d of a lead frame, and the lead frame and the inner electrodes are connected together with metal wires. Then, a portion of the lead frame which covers the magnetoelectric transducer is molded using a resin. Subsequently, steps including deburring, lead formation, and electromagnetic inspections are executed.
FIGS. 7A and 7B show the appearance of the relatively small element described above as an example of an element produced in the above manner. FIGS. 7A and 7B are a side view and a plan view, respectively. This element has a height h of 0.8 mm and a width w of 1.25 mm. The length L and width W of this element, including a lead frame, are each 2.1 mm.
The smallest commercially available Hall elements, including a lead frame that functions as an external electrode after mounting, have outside dimensions including a height of 0.6 mm on a projected area of 2.5xc3x97l.5 mm or a height of 0.55 mm on a projected area of 2.1xc3x972.1 mm. These elements are characterized by their small height.
To further reduce the size of the element, a tape carrier method that uses no intervening lead frames has been proposed. This method comprises connecting the electrode portion of the magnetoelectric transducer to a tape via bumps to mount it on a substrate. This method is still limited by the thickness of the tape.
The present invention is provided in view of these problems, and it is an object thereof to provide a very thin magnetoelectric transducer that allows the correctness of its mounting to be determined nondestructively, as well as a production method therefor.
It is another object of the present invention to provide a magnetoelectric transducer that allows a magnetoelectric transducer to be easily formed and that is of a pellet size, that is, has a size substantially equal to that of a pellet, as well as a production method therefor.
After wholehearted examinations, the inventors have concluded that notably the size and thickness reductions on the projected area are limited as long as a lead frame such as the one described previously is used. Even if the magnetoelectric transducer has a mold size of about 1.5xc3x971.5 mm, lead frames projecting from the element must be formed so as to be suited for mounting. Thus, these projecting parts pose a problem. Further, since the reduction of the thickness of the lead frames is limited and the front and back sides of the lead frames must be covered with a mold resin, the reduction of the height is limited.
The present invention is based on this conclusion, and makes the size of the entire magnetoelectric transducer, including mounted electrodes, substantially equal to the mold size.
That is, a magnetoelectric transducer according to the present invention is characterized in that the element comprises a magnetosensitive section and internal electrodes formed on an upper surface of any insulating substrate having conductive layers formed on side surfaces thereof, an insulating portion and each of the conductive layers are formed of a sintered compact, the sintered compact of the conductive layer is mainly composed of metal of a high melting point of 1,600xc2x0 C. or higher and ceramic powders, and the sintered compact of the conductive layer contains 10% to 90% of the high-melting-point metal.
Further, the magnetoelectric transducer according to the present invention is characterized in that the high-melting-point metal is W, Mo, Ta, or a mixture thereof, and the sintered compact of the insulating layer is a substrate composed of alumina.
Furthermore, the magnetoelectric transducer according to the present invention is characterized in that an adhesive resin layer or an inorganic layer is formed on a upper surface of the insulating substrate, and the magnetosensitive layer and each of the internal electrodes are formed thereon.
Moreover, the magnetoelectric transducer according to the present invention is characterized in that the sintered compact of the conductive layer and each internal electrode, separated from each other at least via a step of the adhesive resin layer or the inorganic layer, are electrically connected together using a conductive resin or a metal material.
Further, the magnetoelectric transducer according to the present invention is characterized in that an inorganic layer is formed on the upper surface of the insulating substrate, and an InSb-based thin film having an electron mobility of 10,000 cm2/V/sec. or more is formed on the inorganic layer. The inorganic layer may be made of silica, alumina, or glass.
Furthermore, the magnetoelectric transducer according to the present invention is characterized in that a resin layer is formed on the upper surface of the insulating substrate, and an InSb-based thin film having an electron mobility of 20,000 cm2/V/sec. or more is formed thereon.
Moreover, the magnetoelectric transducer according to the present invention is characterized in that a metal coat is formed at least on a surface of the sintered compact of the conductive layer.
Further, the magnetoelectric transducer according to the present invention is characterized in that a strain buffering layer is formed on the magnetosensitive section, and a protective film is formed thereon.
Furthermore, a method for producing a magnetoelectric transducer according to the present invention is characterized by comprising the steps of forming a thin film that senses magnetism, on a surface of an insulating substrate via an insulating layer, the substrate having a conductive layer formed therein and mainly composed of a high-melting-point metal layer and ceramic powders in a thickness direction of the substrate, a sintered compact of each of the conductive layers containing 10% or more to 90% of the high-melting-point metal; forming a large number of magnetosensitive sections and internal electrodes of metal on the thin film in a pattern of final elements to collectively form a large number of magnetoelectric transducers; cutting the insulating layer on the conductive layer of the substrate; electrically connecting the internal electrodes and conductive layers of each of the magnetoelectric transducers together; forming a protective layer at least on the magnetosensitive section; and cutting a central portion of each of the conductive layers of the substrate to individualize a large number of magnetoelectric transducers.
Moreover, a method for producing a magnetoelectric transducer according to the present invention is characterized by comprising the steps of forming a thin film that senses magnetism, on a surface of an insulating substrate via an insulating layer, the substrate having a conductive layer formed therein and mainly composed of a high-melting-point metal layer and ceramic powders in a thickness direction of the substrate, a sintered compact of each of the conductive layers containing 10% to 90% of the high-melting-point metal; forming a large number of magnetosensitive sections and internal electrodes of metal on the thin film in a pattern of final elements to collectively form a large number of magnetoelectric transducers; etching the insulating layer on the conductive layers of the substrate; electrically connecting the internal electrodes and conductive layers of each of the magnetoelectric transducers together; forming a protective layer at least on the magnetosensitive section; and cutting a central portion of each of the conductive layers of the substrate to individualize a large number of magnetoelectric transducers.
Further, a method for producing a magnetoelectric transducer according to the present invention is characterized by comprising the steps of forming an insulating layer on that part of a surface of an insulating substrate which is different from surfaces of conductive layers formed in the substrate and mainly composed of a high-melting-point metal layer and ceramic powders in a thickness direction of the substrate, a sintered compact of each of the conductive layers containing 10% to 90% or less of the high-melting-point metal; forming a thin film that senses magnetism, on said insulating layer; forming a large number of magnetosensitive sections and internal electrodes of metal on the thin film in a pattern of final elements to collectively form a large number of magnetoelectric transducers; electrically connecting the internal electrodes and conductive layers of each of the magnetoelectric transducers together; forming a protective layer at least on the magnetosensitive section; and cutting a central portion of each of the conductive layers of the substrate to individualize a large number of magnetoelectric transducers.
Furthermore, the method for producing a magnetoelectric transducer according to the present invention is characterized by further comprising the step of coating metal suited for soldering, at least on the conductive layers of the magnetoelectric transducer which are exposed by cutting.
With the above configuration, a very small and thin magnetoelectric transducer having, for example, a height of 0.35 mm on a projected area of 0.8xc3x971.55 mm can be achieved by a simple method.
For a Hall element, which is an example of the magnetoelectric transducer of the present invention, the thin film constituting the magnetoelectric transducer and sensing magnetism can be selected from a group comprising thin compound semiconductor films of indium antimony, gallium arsenic, indium arsenic, and the like or thin three- and four-element compound semiconductor films of (indium, gallium)-(antimony, arsenic). What is called a quantization effect element can also be used. These thin compound semiconductor films are formed on an insulating substrate having conductive layers formed in the thickness direction thereof. The thin compound semiconductor film may be formed on an inorganic layer previously formed on the insulating substrate. Alternatively, a mask is applied to the conductive layers of the insulating substrate to form an inorganic layer, and the thin compound semiconductor film is then formed thereon. In this case, the thin compound semiconductor film is formed directly on the masked conductive layer.
A more sensitive Hall element may be obtained by forming a thin film on a high crystalline substrate by vapor deposition and transferring the thin film to the above-described substrate via a resin. The inventors have proposed various vapor deposition processes for increasing the mobility of indium antimony, that is, its sensitivity, and a thin film produced by these methods is preferably applicable to the present invention (refer to Japanese Patent Application Publication Nos. 1-13211, 1-15135, 2-47849, and 3-59571).
Elements other than the Hall elements include, for example, magnetoresistive elements of ferromagnetic substance, GMRs, and semiconductor magnetroresistive elements. Films for GMRs and magnetroresistive elements of ferromagnetic substance may comprise a ferromagnetic material such as Nixe2x80x94Fe or Nixe2x80x94Co. Further, for semiconductor resistance elements, the above-described compound semiconductor can be used.